This invention relates variously to techniques for comminuting polymeric foams, to techniques for preparing polymeric foams containing that comminuted foam, and to the resulting comminuted foam powder and product polymeric foams. The procedures may be used on foams containing production contaminants such as polyolefins, paper, and foam skins and on other foams containing consumer contaminants such as wood, metal, leather, etc.
Polymeric foams include a wide variety of materials, generally forming two-phase systems having a solid polymeric phase and a gaseous phase. The continuous phase is a polymeric material and the gaseous phase is either air or gases introduced into or formed during the synthesis of the foam. Some of these gases are known as xe2x80x9cblowing agents.xe2x80x9d Some syntactic polymeric foams contain hollow spheres. The gas phase of syntactic foams is contained in the hollow spheres that are dispersed in the polymeric phase. These spheres can be made of a variety of materials including glass, metal, carbon and polymers. Other materials such as fillers, reinforcing agents, and flame retardants can be used to obtain specific foam properties. Polymeric foams, open-celled or closed-cell, are usually classified as flexible, semi-flexible, semi-rigid, or rigid. Flexible foams, foams that recover after deformation, are typically used in carpet backing, bedding, furniture and automotive seating. Rigid foam, foams that do not recover after deformation, are used in thermal insulation, packaging, and load bearing components. Examples of polymers commonly used in foams include epoxy, fluoropolymer, latex, polyisocyanurate, polyimide, polyolefin, polystyrene, polyurethane, poly(vinyl chloride) (PVC), silicone, and urea-formaldehyde.
Typical foam manufacturing processes result in polymeric foam wastes. For example, commercial procedures resulting in large quantities of polyurethane foam produce slabstock in a continuous pouring process. The resulting cast buns are often cut, for example, in pieces that are 1 to 2.5 m wide, 1.5 m high, and as long as 70 m. Foam buns are also made in boxes using batch processes. In either process, the outside of the bun is lined with a paper and/or plastic release sheet, and a layer of foam skin is formed there. The buns generally require trimming of the top and sides before the buns are cut or sliced for commercial use. These top and side trimmings include a foam waste product containing production contaminants.
By xe2x80x9cproduction contaminantxe2x80x9d we mean to include materials that are co-produced or used in the manufacture of slabstock or box foam, and are typically present in the scrap trimmed from the sides, top, and bottom of slabstock or box foam. Examples of production contaminants are those foam skins discussed above. Additionally, the term includes the release sheets or separators also discussed above, that are, e.g., of paper, paper coated with wax or polyolefin, and also may be of film, sheet, or netting made from polymer materials such as polyethylene, polypropylene, polystyrene, or other polyolefins. We will generically nominate the release sheets containing some amount of any polymer as xe2x80x9cpolymeric sheetsxe2x80x9d. The skin material in trimmed scrap (or, xe2x80x9cfoam skinsxe2x80x9d) is quite different in consistency and density from the desired foam product. The skin material is a tougher, more rubbery product, and has a higher density than the desired foam product. Foam skins are layers of non-foam or very high density foam that are formed during the foam polymerization procedures. Foam skin is also present in scrap such as xe2x80x9cmushroomsxe2x80x9d of material from foam molding operations that escape the mold. Foam skin is also found in off-spec molded parts.
Trimmings also result from foam fabrication processes in which useful shapes are cut from the buns. This type of waste is called fabrication scrap, and it generally contains lower amounts of production contaminants than waste from trimming buns.
Polymeric foam waste is also present in many discarded foam-containing products such as furniture, automobile seats, thermal insulation foams, and packaging foams. This type of waste is called xe2x80x9cpost-consumer wastexe2x80x9d. Post-consumer waste often contains contamination from other materials that were used in a fabricated part with the foam or from materials the foam was exposed to during its useful lifetime. These xe2x80x9cconsumer contaminantsxe2x80x9d include wood, ferrous metal, non-ferrous metal, textiles, leather, glass, dirt, oil, grease, adhesives, minerals, and plastics.
xe2x80x9cPolyurethanexe2x80x9d (PUR) describes a general class of polymers prepared by polyaddition polymerization of diisocyanate molecules and one or more active-hydrogen compounds. xe2x80x9cActive-hydrogen compoundsxe2x80x9d include polyfunctional hydroxyl-containing (or xe2x80x9cpolyhydroxylxe2x80x9d) compounds such as diols, polyester polyols, and polyether polyols. Active-hydrogen compounds also include polyfunctional amino-group-containing compounds such as polyamines and diamines. An example of a polyether polyol is a glycerin-initiated polymer of ethylene oxide or propylene oxide.
xe2x80x9cPUR foamsxe2x80x9d are formed via a reaction between one or more active-hydrogen compounds and a polyfunctional isocyanate component, resulting in urethane linkages. As defined here, PUR foam also includes polyisocyanurate (PIR) foam, which is made with diisocyanate trimer, or isocyanurate monomer. PUR foams are widely used in a variety of products and applications. These foams may be formed in wide range of densities and may be of flexible, semi-flexible, semi-rigid, or rigid foam structures. Generally speaking, xe2x80x9cflexible foamsxe2x80x9d are those that recover their shape after deformation. In addition to being reversibly deformable, flexible foams tend to have limited resistance to applied load and tend to have mostly open cells. xe2x80x9cRigid foamsxe2x80x9d are those that generally retain the deformed shape without significant recovery after deformation. Rigid foams tend to have mostly closed cells. xe2x80x9cSemi-rigidxe2x80x9d or xe2x80x9csemi-flexiblexe2x80x9d foams are those that can be deformed, but may recover their original shape slowly, perhaps incompletely. A foam structure is formed by use of so-called xe2x80x9cblowing agents.xe2x80x9d Blowing agents are introduced during foam formation through the volatilization of low-boiling liquids or through the formation of gas during the reaction. For example, a reaction between water and isocyanate forms CO2 gas bubbles in PUR foam. This reaction generates heat and results in urea linkages in the polymer. Additionally, surfactants may be used to stabilize the polymer foam structure during polymerization. Catalysts are used to initiate the polymerization reactions forming the urethane linkages and to control the blowing reaction for forming gas. The balance of these two reactions, which is controlled by the types and amounts of catalysts, is also a function of the reaction temperature.
Effective recycling technologies are highly desirable in order to re-use the foam waste, to maximize the raw material resources of these foams, to reduce or to eliminate the adverse environmental impact of polymeric foam waste disposal, and to make polymeric foam production more cost-effective.
It is desirable to recycle flexible PUR foam by reducing that foam scrap to particles having a maximum particle size of about 2 mm and introducing the comminuted particles in making new flexible PUR foam, see for example U.S. Pat. No. 4,451,583, to Chesler. In the Chesler process, the comminuted particles are added to the reaction mixture for the new PUR, or to one of the reactive liquid components such as the polyhydroxyl compounds, and then new flexible foam is prepared in a conventional manner. Cryogenic grinding is disclosed in the ""583 patent as a preferred grinding technique for forming the required foam scrap particle size.
U.S. Pat. No. 5,411,213, to Just, shows a process for grinding polymers such as PUR by adding an anti-agglomeration or partitioning agent and subjecting the material to a compressive shear force using for example a two-roll mill. In another technique, disclosed in U.S. Pat. No. 4,304,873, to Klein, micro-bits of flexible PUR foam are prepared by subjecting shredded flexible PUR foam and a cooling fluid, such as water, to repeated impact by a plurality of impact surfaces. In yet another technique, U.S. Pat. No. 5,451,376, to Proska et al, discloses a PUR foam comminution process and apparatus wherein a fine comminution is carried out by forcing a mixture of coarsely comminuted material and one of the liquid PUR reaction components through one or more nozzles.
Used foam objects, such as automobile cushioning materials, may be contaminated with grease or oil contaminants that destabilize the formation of new foam. U.S. Pat. No. 5,882,432, to Jody et al, describes a process for directly removing oil or grease contaminants from large PUR foam pieces.
Foam trimmings containing polymeric foam skin waste material, which is typically formed in slabstock on the outside of a foam bun, are difficult to grind effectively using conventional grinding conditions that are most suitable for grinding polymeric foam. The thermal insulating properties of foam make it difficult continuously to grind the foam in relatively long production runs because the grinding temperature tends to increase as grinding is continued, potentially resulting in thermal degradation of the polymeric foam. Production contaminants result in increased grinding temperatures. Furthermore, foam pieces and foam powder are difficult materials to handle in large quantities because these products bridge readily in various processing equipment. Moreover foam powder tends to coat the surfaces of processing equipment such as conveyers, mills and screens.
It is also difficult to grind production foam trimmings for re-use as foam powder because they are typically contaminated with production contaminants such as plastic film or sheeting (often of polymers such as polystyrene or polyolefins such as polyethylene and polypropylene), plastic netting, or paper, which are used in slabstock production. These plastics may coat the grinding surfaces of the comminution equipment because of the heat generated during grinding processes. Paper contamination hinders comminution of foam, particularly when comminuting to obtain very small foam particles, because the grinding properties of paper are very different from those of polymeric foam. The papers may also be coated with a polymer. Large particles of these contaminants cause processing difficulties with subsequent foam production and cause quality problems with the resulting foam. These problems include: high viscosity of PUR-foam ingredients that include mixtures, such as slurries, of foam powder and active-hydrogen compounds, poor cell structure in the resulting foam, visibility of the larger foam particles, and poor quality and feel of the foam.
Foam scrap that is contaminated with adhesives is difficult to process using conventional techniques for comminuting and conveying the resulting foam pieces or foam powder. Adhesives often cause foam pieces or foam powder to adhere to each other and to conveying and/or processing equipment such as mills. Adhesives present in foam powder that is used to prepare new foam can destabilize the polymer foam during its formation.
Cost-effective improved techniques, methods, and equipment for processing polymeric foam to achieve improved integration of polymeric foam and foam powder processing steps, utilization of a wider range of foam compositions for comminution and re-use in new foam, improved control and reliability of processing equipment and methods, reduction of operating and materials costs and improvements in resource utilization are all desirable. Particularly, a need exists for improved processing techniques and devices for (1) comminuting polymeric foam including production contaminants such as polymeric foam skins, polymeric sheet, or paper, (2) preventing or reducing excessive heating of polymeric foam during comminution, (3) processing foam products containing a wide variety of production and consumer contaminants and (4) using foam powder prepared from polymeric foam including production and consumer contaminants as an ingredient in new foam.
None of the documents cited above disclose the inventive processes and foam products described herein.
This invention provides novel methods and devices for polymeric foam processing, particularly methods for comminuting (e.g., milling, pulverizing, or grinding) polymeric foams, preferably those containing with production and, perhaps, post-consumer contaminants. These novel methods and devices reduce excessive heating of polymeric foam during processing and improve the processing of polymeric foam products containing a variety of contaminants.
Polymeric foams containing production contaminants are comminuted on a two-roll mill. The resulting comminuted foam powder is quenched both to cool the comminuted foam powder and the comminution process equipment.
In one variation of the present invention, a novel collection chamber is employed variously for collecting polymeric foam powder from a two-roll mill and for quenching the comminuted foam powder by means of a gaseous cooling medium.
Another variation of the invention involves a novel sifter for screening polymeric foam powder. The device employs a cylindrical screening tube and beater bars for separating foam particles from larger foam pieces.
The PUR foam powder prepared from PUR foam containing production contaminants such as PUR foam skins, polymeric sheets (often of polyethylene, polypropylene, or polystyrene), and paper (perhaps coated) is subsequently used in the preparation of new PUR foam.
In yet another variation of the present invention, a novel energy optimizing method for a two-roll mill is employed wherein the fastest roll is driven, for example, by an electric motor while the slowest roll is indirectly driven by the first roll through friction between the two rolls.
In another variation of the present invention a novel feed rate control method is employed for controlling the rate at which polymeric foam pieces are fed to a mill. This novel method uses, e.g., the mill""s power consumption, to control the rate at which conveying equipment feeds foam pieces to the mill.
The inventive procedure includes procedures for removing oil and grease from foam powder and either removing adhesive contaminants from polymeric foam powder or destroying the adhesive property of these contaminants.